There are many examples of tags. In recent years electronic tags have been developed which store data and from which data can be retrieved by way of radio frequency (RF) or capacitive interrogation. These so-called smart tags are sophisticated often having their own energy supply or a means for deriving energy from an interrogator usually by way of inductive or capacitive coupling. Such smart tags are extremely effective at performing their intended purpose, but they are complex and expensive.
According to the first aspect of the invention there is provided a tag comprising: a container, in which there is at least one particle, arranged to be displaced with respect to the container so that a radio frequency (RF) signature is emitted; said RF signature being capable of identifying the tag
The generation of electric charge by contact between two surfaces is known as the Triboelectric effect. The static charge is not caused directly by friction but by adhesion between two surfaces at molecular level. Surfaces stick together because chemical bonds form. When surfaces in contact separate these bonds rupture and any asymmetrical bonds tend to leave a charger imbalance due to an interchange of electrons between the surfaces.
The inventors have determined that use can be made of this effect to provide a tagging system, which is very sensitive to movement.
The tag described herein allows for a very low cost and simple means to apply tagging. Specifically it provides a cheap and simple means to generate a tagging signal. The invention will now be described in more detail.